Embodiments of the present invention relate generally high-speed serial data communication devices and, more specifically, to an eye viewer architecture that may be utilized for eye monitoring of high-speed serial signals.
This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present invention, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present invention. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
In high-speed serial interface (HSSI) applications, a high-speed serial input signal sent to a receiver (RX) portion of a transceiver of an integrated circuit (IC) device may become attenuated and distorted due to frequency-dependent signal loss across interconnects. For example, one form of distortion that may affect the input signal is intersymbol interference (ISI), which occurs when one data bit of the serial signal interferes with a subsequent data bit. Accordingly, increases in ISI rates may produce a measurable degradation of the input signal quality, which may negatively affect the margins of clock and data recovery (CDR) circuitry.
A variety of RX equalization and signal modeling techniques have been explored to improve the RX input signal before reaching clock and data recovery circuitry in the RX. For example, one technique for evaluating ISI in a high-speed serial input signal involves observing an eye diagram associated with the signal. An eye diagram may result when the waveform of each data bit of the signal is superimposed onto a single bit time interval, or unit interval (UI). Typically obtained by probing the high-speed serial input signal with an oscilloscope, an eye diagram is so named because the resulting superimposition of the bits of the high-speed serial signal forms the general shape of an open eye. A higher-quality serial signal generally has a more “open” eye diagram, while a lower-quality serial signal generally has a more “closed” eye diagram.
An eye diagram may enable designers or field engineers to visualize and correct for some ISI of a high-speed serial input signal, as well as other jitter compounds of the signal. However, an IC may generally include equalization circuitry to improve the quality of the signal, the output of which may be internal to sensitive high-speed nodes that may be difficult, if not impossible, to probe with an oscilloscope. Moreover, with or without equalization circuitry, any internal serial signals may become distorted by the RX circuitry or by on-die connections. As such, the ISI of the post-equalization signal or of other internal serial signals are typically difficult to visualize.